Photo: reutersPro-Russian armed separatists have seized five armoured personnel carriers and a tank from the Ukrainian army, which they then drove in a victory lap through the centre of Kramatorsk in Ukraine's east, where government forces are attempting to wrest back control of the city, azh.kz reports.

About 100 heavily armed men, some in balaclavas and wearing military fatigues, rode on top of the seized armoured vehicles, the first of which was flying a Russian tricolour. Several hundred locals gathered around the convoy, cheering, tooting their car horns and waving in support as it rolled past Kramatorsk's railway station, not far from the airfield where Ukrainian soldiers clashed with separatists on Tuesday.

Ukrainian military helicopters hovered above the dramatic scenes in central Kramatorsk but there seemed to be no attempt by government forces to try to wrest back control of the situation.

The mayor of Slavyansk said the pro-Russian local people there were being supported by unmarked troops from Russia and Crimea. Turchynov gave pro-Russians in eastern Ukraine until Monday morning to give up their arms and the buildings they had seized, but instead a pro-Russian mob took over yet another government building in Horlivka that day. A man who appointed a new police chief there later said he was a lieutenant colonel in the Russian army.

General Vasily Krutov, the commander of the Ukrainian operation in the region, said the government's ultimatum would not be extended. That would be "too humanitarian", he said. He added that civilian casualties were possible but his forces would try to make sure "not one innocent person suffers".

He said: "Unfortunately we face a difficult situation because those realising their plan are hiding behind human shields" – an apparent reference to the many pro-Russian local people who have taken part in taking over buildings. "Some of them are cynically working towards their own ends, but many are under the influence of propaganda," he said.

The UN human rights office, meanwhile, said ethnic Russians in eastern Ukraine had falsely claimed to be under assault to justify Russian intervention, warning that such propaganda could affect Ukraine's presidential election next month.

Russiacondemned the report, saying it was one-sided and seemed to have been "fabricated" to fit pre-formed conclusions.